Numerous businesses and other organizations mail large quantities of mail, such as bills, statements and computer-generated letters, and “pre-sort” the mail in mail sorters. In the United States, for example, in order to obtain a discounted rate for first class mail, mailers must ensure that the mail meets a set of requirements for “automation mail.” Foremost among these is that the mail must be presented to the U.S. Post Office (USPS) in trays that are “sorted.” Each tray must contain a minimum number of envelopes in one of the following categories: (1) all envelopes will be mailed to the same 5-digit ZIP-code; (2) all envelopes will be mailed to the same 3-digit ZIP code (that is, the first three digits of the ZIP code are the same); (3) all envelopes will be mailed to the same Automated Area Distribution Center (AADC) (which is a grouping of several ZIP codes determined by the USPS); or (4) all envelopes will be mailed to the same Mixed AADC (which is a grouping of AADCs designated by the USPS). Each of these categories receives a different discount, currently ranging from $0.098 for category (1) to $0.05 for category (4). In some other countries, similar sortation requirements exist, although the details vary.
For large volume mailers who might mail from 100,000 to over 5,000,000 envelopes a day, financial reasons dictate taking steps to obtain these discounts by sorting and otherwise qualifying the mail to be automation mail.